Part of Speech: Noun

Definition:an ugly, twisted expression on a person’s face, typically expressing disgust, pain, or wry amusement.

Source: Words at Dictionary

All American Girl by Julia Alvarez, line 5

“trying to match my face/with words in my new language: grimace, leer,/disgust, disdain-feelings I had yet to feel “

The word “Grimace” means expressing disgust, or pain from reading the line in the poem I think it’s easy to get an idea that the word has a negative meaning close to disgust and disdain.